Heretofore, many attempts have been made to develop catalyst components for polymerization of olefins which exhibit a high catalytic activity in the production of polyolefins such as polypropylene having a high stereoregularity. Recently, there are known many solid catalyst components improved in catalytic performance. They are produced by contacting a compound of a transition metal belonging to Groups IVb to VIII of the Periodic Table of the elements with a variety of compounds which function as the carrier.
The performance of a polymerization catalyst is greatly affected by a cocatalyst with which the solid catalyst component is combined. Heretofore, the common cocatalyst has been a combination of an organoaluminum compound and an organic acid ester.
In order to maximize catalytic performance, researches have been made on cocatalysts to some extent. For example, it has been disclosed that organic acid esters may be replaced by an electron donor compound containing a hetero atom. Such an electron donor compound is exemplified by nitrogen-containing compounds (e.g., piperidine, pyridine, and nicotinic ester), sulfur-containing compounds (e.g., thiophenic ester), and phosphorus-containing compounds (e.g., phosphites and phosphates). It is also disclosed that a trialkyl aluminum compound and a halogen-containing organoaluminum compound may be used in combination with each other as the organoaluminum compound.
However, the improvements in catalytic performance achieved by the above-mentioned methods are not so significant as those achieved with commonly used cocatalysts composed of a trialkyl aluminum and an organic acid ester. An electron donor compound containing a hetero atom tends to decrease the catalytic activity or the stereoregularity of catalyst.
There is disclosed in Japanese Patent Laid-open No. 139511/1981 a new catalyst in which a solid catalyst component is combined with a cocatalyst composed of a trialkyl aluminum and a hindered Lewis base and an unhindered Lewis base. It has been found that this catalyst exhibits a high catalytic activity and high stereoregularity; but it does not completely outperform the conventional catalyst incorporated with a cocatalyst.